Method and device for identifying knocking

ABSTRACT

A method and a device for detecting knocking, in which a measurement signal of a knock sensor is evaluated during combustion in a cylinder of a combustion engine to determine whether the combustion occurred with knocking. The measurement signal is subdivided into a plurality of windows, and in each window an examination is performed to determine whether the combustion occurred with knocking. For a final assessment of whether the combustion occurred with knocking, the events of windows are compared to each other.

FIELD OF THE INVENTION

The present invention is directed to a method and a device for detectingknocking.

BACKGROUND INFORMATION

German Patent No. DE 4027354 describes a method and a device fordetecting knocking, in which a measuring signal of a knock sensor isexamined in a measuring window during a combustion process in a cylinderof an internal combustion engine. The examination determines whether thecombustion occurred with knocking. Knocking combustion in the cylinderof an internal combustion engine refers to an uncontrolled combustionprocess, in particular a combustion process in which controlled ignitionof the combustion mixture by an ignition spark does not occur, butrather self-ignition occurs. With such knocking combustion, unacceptablyhigh pressures or temperatures occur in individual parts of thecombustion chamber, and there is danger of damage to the internalcombustion engine. The sense and purpose of a method or device fordetecting knocking is therefore to operate the internal combustionengine in an operating range in which knocking combustion is avoided. Onthe other hand, operation as close as possible to this zone of knockingcombustion is desirable, since the combustion process occursparticularly economically and cleanly there.

SUMMARY

A method and the device according to an example embodiment of thepresent invention for detecting knocking may have the advantage that theaccuracy of the knock detection is improved. In particular, it makes itpossible for individual events that occur during the combustion processto not be judged erroneously as knocking signals. This is particularlyadvantageous in direct-injection gasoline engines, since valves and thelike are operated there during the combustion process, and as a resultinterfering noises are produced that impair knock detection. The methodaccording to the present invention is also particularly advantageous ifthe cylinder of the combustion engine is operated using a piston thathas a high center of gravity (top-heavy piston). In the case of suchpistons, a tilting motion occurs in the area of the top dead centerpoint, which also results in interfering noises.

A particularly certain decision regarding the presence of knocking ornon-knocking combustion may be made if three windows are examined, thecombustion necessarily being detected as knocking in at least twowindows. The time width of the windows may be specified in a fixed or avariable manner. In the case of a variable time width, it may beparticularly advantageous to provide for speed-dependence, in order totake into account the greater changes in combustion at higher speeds. Inaddition, gaps may also be provided between the windows, in particularif an interfering signal occurs at a predictable point in time.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the present invention are illustrated in thefigures and explained in greater detail in the following description.

FIG. 1 shows the course of a measuring signal.

FIG. 2 schematically shows a device for detecting knocking.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

In combustion chambers of combustion engines, abnormal combustionprocesses may occur which are referred to as knocking. This knockingresults from self-ignition of the combustible mixture, which is not yetaffected by the flame front that is spreading out from the spark plug.With such knocking, strong pressure or temperature peaks which maydamage the cylinder or piston occur at individual locations in thecombustion chamber. The frequency of such knocking combustions dependson the operating state of the internal combustion engine. Despite thetendency for knocking combustion, operation in this zone is desirable,since the combustion there is particularly efficient and low inpollutants. The knocking event is manifested as pressure fluctuations inthe cylinder, which subside as the combustion process continues.Knocking thus does not occur at an individually defined point in time,but is manifested as a vibration that is observable in a period of time.The observation is made by knock sensors, which detect a signal thatderives from the pressure variations in the cylinder. Conventional knocksensors are designed, for example, as structure-borne sound sensors,i.e., as acceleration sensors which are attached to the engine block.The pressure peaks in the combustion chambers produce sound waves in theengine block, which are detected by these acceleration sensors. Inaddition, some conventional knock sensors deduce a pressure signal fromthe combustion chamber directly. In the case of structure-borne soundsensors in particular, other events may also result in a signal.Suitable for this are all events that produce a structure-borne soundsignal in the engine block, such as operation of valves or the like.

FIG. 1 shows an example of a signal of a knock sensor, for example anacceleration sensor or a pressure sensor. The intensity of this signalis plotted on the B axis. The time slope is plotted on the A axis. InFIG. 1, the time is plotted on the A axis. Alternatively, the crankshaftangle could also be plotted here. The diagram in FIG. 1 thus depicts theintensity of the measuring signal over time. As may be seen from FIG. 1,the knock signal is manifested as an irregular vibration, whichdecreases in intensity over time.

FIG. 1 portrays a knocking signal, i.e., the intensity fluctuations arerelatively high. In the case of a non-knocking signal, the intensityfluctuations would be significantly smaller.

Also recorded in FIG. 1 are a plurality of time windows 11, 12, 13, eachof which represents a measuring window. The knocking signal is examinedin each of these measuring windows to determine whether knockingcombustion is involved. The signal course portrayed in FIG. 1 representsthe knocking signal of a single combustion process. A predefined timewindow is usually specified for the examination of whether thecombustion occurred with knocking. To let the signal become as strong aspossible, the longest possible measuring range is of interest; i.e.,normally depicted measuring windows 11, 12, 13 are considered togetherin order to form an overall signal. The assessment of whether thecombustion occurred with knocking is then made on the basis of thisoverall signal. The length of this overall range is normally designed tobe as long as a knocking signal is reasonably detectable. According tothe present invention, it is proposed to further subdivide thereasonable measuring range, in particular into a plurality of windows11, 12, 13. Within each of these individual windows 11, 12, 13, aseparate determination is made of whether knocking combustion occurred.By comparing the results thus found, a final result is then formed whichcontains a statement about whether knocking combustion occurred. Ifthree windows 11, 12, 13 are provided for the measurement, as in FIG. 1,it is advantageous to identify a knocking event only if knockingcombustion was detected in at least two of the three windows 11, 12, 13.Knock detection may thus be improved by this procedure. In particular,individual strong signals that occur in only one of windows 11, 12, 13may be rejected as implausible. As described above, such individualsignals may occur as a result of additional events in the combustionengine. Such an event may be, for example, the closing of a fuelinjector in a direct-injection combustion engine. Furthermore, in thecase of top-heavy pistons, tilting motions may occur in the vicinity ofthe top dead center point, which also may result in an individual strongpulse in the knocking signal during the combustion signal. However, suchan individual event occurs only at a single moment during the course ofcombustion, i.e., a corresponding signal occurs only in a single window.The intensity of these signals may be very high, however, so that in anoverall analysis of all three windows, a knocking signal woulderroneously be concluded.

FIG. 2 shows an example of a device for processing knocking signals. Thedevice for processing knocking signals 1 has a plurality of inputs, thesignals from a plurality of knock sensors 2 being fed to each input.This plurality of knock sensors 2 may be, for example, structure-bornesound sensors, which are implemented, for example, as piezoelectricacceleration sensors. Knock sensors 2 are assigned to differentcylinders, and are attached to the engine block at places where they areable to effectively receive the signals for the particular cylinders. Aconfiguration as in FIG. 2, having two knock sensors 2, is good forexample for measuring knocking signals in a four cylinder engine. Sincethe combustions do not occur simultaneously but sequentially, thesignals from the individual knock sensors may be processed sequentiallyby the device for knocking detection 1. To this end, the signals fromknock sensors 2 are fed to the device for knocking detection 1. Using amultiplexer 3, these signals which are present at the inputs are readappropriately by the inputs which are assigned to different knocksensors 2. Positioned downstream from multiplexer 3 is an amplifierstage 4, in which an amplification of the knocking signals occurs.Positioned downstream from amplifier stage 4 is a filter 5. Filter 5 isdesigned as a bandpass filter, since knocking signals occur only in acertain frequency range. The output signal from filter 5 is fed to arectifier 6, in which the signals are rectified. This rectifier isnecessary because the knocking signals may be either positive ornegative and only the absolute intensity is of interest. Downstream fromrectifier 6 is an integrator 7, in which the rectified signals areintegrated over a predefined time period. The signal thus integrated isa measure of the knock intensity, and is emitted by the device fordetecting knocking. In another unit, for example in the control device,which is not shown here, this integrated knock intensity value is thencompared to a reference value.

The integration in integrator 7 normally occurs over the entire timeperiod, i.e., the entire time period in which knock signals may occur isconsidered for each combustion process. According to the presentinvention, integrator 7 is now activated in such a way that instead ofone integrated signal over the entire time period, three differentsignals are emitted sequentially, each signal corresponding to anintegration in windows 11, 12, and 13. These are then comparedindividually to reference values, and the comparison to the referencevalue is used to determine whether a knocking combustion process ispresent in particular window 11, 12, 13. The reference values to whichthe integrated signals for individual windows 11, 12, 13 are comparedmay vary, and in particular may differ in their height. Thus threesignals are produced, each signal representing a measure of knockingintensity and being evaluated to determine whether knocking is present.This approach makes it possible to reliably detect in particularindividual events that result in an increase in the knocking signal inonly one of windows 11, 12, 13 as signal parts that are not based onknocking. It is typical of knocking combustion that knocking is detectedin all three windows.

In the description of FIG. 1 it was assumed that windows 11, 12, 13 aredefined as time periods. These time periods may be predefined in a fixedmanner, i.e., the signal is integrated for individual predefined timeperiods 11, 12, 13. This has the advantage that it is particularlysimple. The time duration of these windows 11, 12, 13 may also bevariable, however; in particular, it is also possible to make theduration of these measuring windows dependent on the rotational speed.In that case the duration of each of these windows 11, 12, 13 would beshorter, in particular at higher speeds, since the combustion processesproceed more quickly due to the faster motion of the piston.

In addition, windows 11, 12, 13 may be defined not as time periods butas crankshaft angles. This means that in FIG. 1 axis A would not be atime axis but a crankshaft angle axis. However, in this case it wouldnot be necessary to shorten the windows as a function of an increasingrotational speed, since this is already accounted for by the definitionof windows 11, 12, 13 as ranges of the crankshaft.

In FIG. 1, the time duration of all of windows 11, 12, 13 is the same.If it is necessary and practical, the durations of these measuringwindows may also differ. In particular window 13, which comes much laterin time than the beginning of combustion, when the signal intensitieshave already dropped significantly, could be lengthened to achieve agreater measuring signal.

Furthermore, it could be determined that a knocking event is alwaysdetected in one of windows 11, 12, 13. This is particularly serious ifthe combustion engine is operated by the engine control unit in a rangein which knocking is actually not expected. In such a case, it couldthen be concluded that a signal is involved here which is not caused byknocking. Using additional measurements, it could then be determinedwhere this signal always occurs, and measuring windows 11, 12, 13 couldbe placed so that measuring does not occur at the times in which theerroneous signal always occurs. Gaps in which no attempt is made tomeasure a knocking signal could also be provided in the measuring range,i.e., a range of time is provided for example between windows 11 and 12.As a result of this measure, it is possible to mask out regularlyoccurring interfering noises such as the opening or closing of a fuelinjector for the purpose of determining knocking in the combustionengine.

1-14. (canceled)
 15. A method for detecting knocking, in which ameasuring signal of a knock sensor is evaluated during combustion in acylinder of an internal combustion engine to determine whether or notthe combustion is taking place with knocking, the method comprising:subdividing the measuring signal into a plurality of time windows;examining each window to determine whether the combustion occurred withknocking; and comparing results of the plurality of windows to eachother for a final assessment of whether the combustion occurred withknocking.
 16. The method as recited in claim 15, wherein the combustionis assessed as occurring with knocking if a knocking combustion isdetected in a majority of the plurality of windows.
 17. The method asrecited in claim 15, wherein the measuring signal is subdivided into atleast three measuring windows, and the combustion is assessed asoccurring with knocking if a knocking combustion is detected in at leasttwo of the windows.
 18. The method as recited in claim 15, wherein alength of the windows is predefined in a fixed manner.
 19. The method asrecited in claim 15, wherein a length of the windows is changed as afunction of a speed of the internal combustion engine.
 20. The method asrecited in claim 15, wherein the windows are defined as one of a timerange or an angle range.
 21. The method as recited in claim 15, whereingaps are provided between the windows, and no examination of whether thecombustion occurred with knocking takes place in the gaps.
 22. A devicefor detecting knocking, in which a measuring signal of a knock sensor isevaluated during combustion in a cylinder of an internal combustionengine to determine whether or not the combustion is taking place withknocking, comprising: an arrangement configured to subdivide themeasuring signal into a plurality of time windows; an arrangementconfigured to examine each window to determine whether the combustionoccurred with knocking; and a comparator to compare results of theplurality of windows to each other for a final assessment of whether thecombustion occurred with knocking.
 23. The device as recited in claim22, wherein the combustion is assessed as occurring with knocking if aknocking combustion is detected in a majority of the plurality ofwindows.
 24. The device as recited in claim 22, wherein the measuringsignal is subdivided into at least three measuring windows, and thecombustion is assessed as occurring with knocking if a knockingcombustion is detected in at least two of the windows.
 25. The device asrecited in claim 22, wherein a length of the windows is predefined in afixed manner.
 26. The device as recited in claim 22, wherein a length ofthe windows is changed as a function of a speed of the internalcombustion engine.
 27. The device as recited in claim 22, wherein thewindows are defined as one of a time range or an angle range.
 28. Thedevice as recited in claim 22, wherein gaps are provided between thewindows, and no examination of whether the combustion occurred withknocking takes place in the gaps.